Sampling and measurement for volatile organic compounds
Download
1 / 12

sampling and measurement for volatile organic compounds - PowerPoint PPT Presentation


  • 253 Views
  • Updated On :

Sampling and Measurement for Volatile Organic Compounds. Types of analytical instruments. Personal Monitors Light weight monitors Can be conveniently carried or worn by a person Portable monitors Can be moved during sampling Stationary monitors Have to be operated from a fixed location.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'sampling and measurement for volatile organic compounds' - ostinmannual


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Sampling and measurement for volatile organic compounds l.jpg

Sampling and Measurement for Volatile Organic Compounds


Types of analytical instruments l.jpg
Types of analytical instruments

  • Personal Monitors

    • Light weight monitors

    • Can be conveniently carried or worn by a person

  • Portable monitors

    • Can be moved during sampling

  • Stationary monitors

    • Have to be operated from a fixed location

Volatile Organic Compounds


Types of sampling l.jpg
Types of Sampling

  • Active Sampling

    • Contaminated air is directly drawn into a sensor or collector

    • Provides a real time analysis of the sample

  • Passive Sampling

    • Air diffuses into the collector

    • Longer period of time must be allowed for accurate results

Volatile Organic Compounds


Sampling methods l.jpg
Sampling methods

  • Principles of Sampling Collectors

    1. Air displacement

    2. Condensation

    3. Gas washing or absorption

    4. Adsorption

Volatile Organic Compounds


Air displacement sampling method l.jpg
Air Displacement Sampling Method

  • Evacuated flasks or plastic bags are used

  • Samples are collected by opening the inlet to the contaminant-laden air

  • Sample is subsequently analyzed using a suitable analytical method

Volatile Organic Compounds


Condensation sampling method l.jpg
Condensation Sampling Method

  • Air is passed through a U-tube or a suitable container

  • Sample is subsequently cooled to below the boiling point of the pollutant

  • In most cases a liquid nitrogen cryogenic trap is used.

  • Condensed liquid is eventually analyzed

Volatile Organic Compounds


Gas washers absorbers sampling method l.jpg
Gas washers/ Absorbers Sampling Method

  • Air containing the pollutants is bubbled through a liquid contained in an impinger

  • An aliquot of the liquid is analyzed to determine the characteristics and concentrations of the pollutants

  • Distilled water is commonly used for readily soluble gases

  • A liquid medium that reacts with the pollutants should be avoided

Volatile Organic Compounds


Gas washers absorbers sampling method8 l.jpg
Gas washers/ Absorbers Sampling Method

  • This method is suitable only for a few specific pollutants such as Formaldehyde, Phenol and Ethylene Oxide

  • Collection Efficiency can be increased by:

    • Decreasing the flow rate

    • Improving the distribution of gas phase in the liquid medium

    • Increasing the residence time

    • Using two or more collectors in series

Volatile Organic Compounds


Adsorption sampling method l.jpg
Adsorption Sampling Method

  • Used for measurement of emissions from materials.

  • Emissions are measured either in an environmental chamber or through “head space” analysis

  • Environmental Chamber Studies:

    • Material is placed in a chamber

    • Environmental parameters of the chamber (temperature, humidity, air exchange rates) are controlled precisely

    • Air samples are collected in solid adsorbent tubes for later analysis with a gas chromatograph

Volatile Organic Compounds


Adsorption sampling method10 l.jpg
Adsorption Sampling Method

  • “Head-Space” analysis

    • Small samples of the material are placed in a container

    • Head space gases are collected and analyzed by a gas chromatograph

    • Sampling time depends on the emission rate from the material

  • Solid adsorption media are more popular

    • Pollutants are allowed to adsorb for a predetermined period of time on a solid

    • Most frequently used solid adsorbent is activated carbon and silica gel

Volatile Organic Compounds


Adsorption sampling method11 l.jpg
Adsorption Sampling Method

  • Factors for successful use of adsorbent cartridges

    • Careful cleaning of the sorbent tube to remove background contamination

    • Accurate determination of sampling rate

  • Cleaning of cartridges

    • Heat them at a high temperature under vacuum or by flowing inert gas through the cartridge

    • Flow of inert gas should also continue during cooling

    • Another method is to wash the cartridge with a solvent and dry it at a temp. of 100-150 oC

Volatile Organic Compounds


Analysis methodologies l.jpg
Analysis Methodologies

  • Colorimeters and Spectrophotometers

    • Used to quantify a specific pollutant

    • Utilize liquid reagents, chemically treated papers and glass indicating tubes

    • Chromotropic acid method

      • Most frequently used to determine the concentration of Formaldehyde

      • Measured volume of sample air is drawn through distilled water into an absorber

      • Collection efficiency greater than 95% is achieved by using two absorbers in series

Volatile Organic Compounds


ad